The closing off of pressure vessels by means of sealing elements, for example by means of covers which enable accessibility to the inside of the pressure vessel without damage to this, is a much dealt-with technical problem which with increasing size of pressure vessels with increasing pressures is constantly repeated. The problem is additionally intensified if the pressure vessel serves not only for the simple storage of a pressurized medium but also has to meet additional requirements. In the case of a turbomachine, for example a turbocompressor, the additional task is set of not allowing the fastening elements for closing off the pressure vessel to collide with other constructional elements. If the cover itself is to furthermore serve not only for closing off the pressure vessel but if necessary also to serve as a carrier of functional components, for example as a carrier of a bearing for the rotor of a turbomachine, which rotor is guided through the cover, wherein by means of a shaft seal the gap between the cover and the rotor is sealed off, special demands are to be made on the rigidity of the cover itself and its fastening so that no undesirable displacements of the functional components take place. A further requirement in the case of particularly large pressure vessels of the previously described type is that in view of the very large weight of a cover for a pressure vessel, installation has to be carried out under limiting conditions which are to be found on a construction site. If in this case the cover at the same time is a carrier of additional functional modules, which in their turn can also have a heavy weight, the requirement for displacements of the cover within the scope of the installation procedure has to be limited to a minimum in order to be able to carry out damage-free installation under realistic conditions.